This invention concerns an apparatus for detecting the color content of a video signal and determining whether it is appropriate to perform aperture correction. In particular, it relates to the detection of skin-tones in a signal representing a color video image and a corresponding reduction or elimination of aperture correction for portions of the image containing those tones.
Aperture correction, also called contour correction or peaking, is a technique in which video signals are processed to emphasize the high frequency components of the signal relative to the low-frequency components. The higher frequency components of the signal correspond to the more sharply defined objects. When adding peaking to a signal, for example, edges of the video image are emphasized.
Psycho-optic experiments have shown that images having clearly defined edges are more pleasing to the human eye. However, more clearly defined wrinkles, blemishes, and poor skin texture are not aesthetically pleasing to the human eye. Thus, it is beneficial to have the ability to selectively perform or omit aperture correction on specific color hues in order to soften the focus on undesirable skin features.
In the television and film industry, previous methods of reducing edge detail in an image have included the placement of a gauzing over the camera lens. While this decreased the clarity of wrinkles and blemishes, it also undesirably decreased the clarity of every other portion of the image.
One method currently in use detects a selected color and brightness and inhibits the application of aperture correction in areas containing the selected color and brightness.
Additional methods of color detection in current use involve the definition of color regions designed to represent the desired colors. In FIG. 1a, the definition of a fleshtone region is illustrated by a rectangular window 110 which covers a range of hues and saturations. In actuality, the fleshtone region 112 is defined by a range of hues, independent of saturation. Thus, the rectangular window 110 covers too wide of a range of hues for low saturation and too narrow of a range of hues for high saturation. Highly saturated fleshtone signals are not detected and aperture correction occurs, resulting in the emphasis of undesirable fleshtones. Additionally, low saturation signals outside the given range of fleshtone hues are designated as fleshtone and aperture correction does not occur for more highly saturated hues in which it is desirable to perform aperture correction. If, for example, part of the area containing the selected color is in shadow while part is in full sun, aperture correction may be applied to the part that is in the shadow (low saturation) but not to the part in the sun (high saturation).
FIG. 1a illustrates an additional problem with current methods. The rectangular color region 110 is defined by hard limits. In other words, a given hue and saturation is either in the defined rectangular color region or it is not. The transition from zero aperture correction within the rectangular color region to full aperture correction outside of the rectangular color region is immediate. If two colors are similar, the color positioned immediately inside the defined rectangular color region is not emphasized while the color positioned immediately outside the color region has its edges fully emphasized.